We propose to develop and demonstrate a novel assay for mimicking the tumor microenvironment. The assay will be built using our patented and commercially available SynVivo family of cell based assays. Tumor drug delivery is a complex phenomenon affected by convective blood transport, high interstitial pressure and enhanced vascular permeability in addition to the drugs physico-chemical properties. Current in vitro models of tumor drug delivery are oversimplified and hence overestimate in vivo performance with poor predictability. Our proposed assay will accurately model the tumor microenvironment encompassing (a) circulation in the vessels, (b) transport across the vessel walls, and (c) tumors cultured in a 3-dimensional environment using a novel hydrogel system. The assay will be designed to study drug administration via intra-tumoral or systemic route. In Phase I, we will design and fabricate prototypes of the microfluidic device followed by co-culture of endothelial and tumor cells/fibroblasts under physiological 3D conditions. Drug efficacy will be assessed using well-characterized therapeutics. Phase II enhancements include assays for organ specific tumors and in vivo validation. A multi-disciplinary (engineering and biology), industry-academic team with substantial expertise in all facets of the proposed study has been assembled for successful execution. The developed assay will have critical applications in basic research for characterizing the tumor microenvironment, and in drug development. The product will be commercialized to pharmaceutical/biotech companies, research labs, universities and non-profit organizations engaged in cancer research and drug delivery.